1. Structural Characteristics
The present invention relates to a gene encoding a human V-ATPase C subunit which was cloned from a human embryonic brain. The length of the gene is 1665 bases. It has two forward open reading frames, which start at position 344 and terminates at position 1489, and encode 381 amino acid residuess. The isoelectric point of human V-ATPase C subunit is pI 6.3. It shares a 62% homology with human vacuolar H+-ATPase C subunit, and bovine vacuolar H+-ATPase C subunit. Therefore it is named as a human V-ATPase C subunit.
2. Function
Human vacuolar H+-ATPase C subunit are known to be able to “pump” ions or protons into organelles in side a cell, or transport ions or protons across plasma membrane (e.g., membranes of osteolast, renal mesenchymal cell). The catalytic site of human vacuolar H+-ATPase is a sexamer composed of three A subunits and three B subunits, and can bind to and hydrolyze ATP. Three additional subunits C, D and E, function as regulatory units. The primary function of human vacuolar H+-ATPase is the regulation of local cytoplasmic pH. It also plays significant roles in receptor-mediated endocytosis, cytoplasmic streaming, protein degradation and coupled transport. Thus, human vacuolar H+-ATPases play an important role in renal acidification, bone reabsorption and cytoplasmic pH stablization. It is obvious that human vacuolar H+-ATPase C subunit, as one of three regulative subunits, regulates the activity of human vacuolar H+-ATPase.
3. Medical Implications
A recombinant human vacuolar H+-ATPase C subunit protein or polypeptide has numerous applications, which include, but are not limited to, direct application for treating diseases caused by lowered or lost vacuolar H+-ATPase C subunit function, and screening for antibody, agonists, antagonists or polypeptides or other ligands that enhance or reduce human vacuolar H+-ATPase C subunit function. For example, an antibody can be used in enhancing or inhibiting human vacuolar H+-ATPase C subunit function, and recombinant which can inhibit or catalyze human may be used to screen for its agonists or antagonists which may be used for medical treatment.
The present invention also provides a method of screening medicaments to enhance (agonist) or inhibit (antagonist) V-ATPase C subunit functions. Agonists may be used to enhance the biological functions of V-ATPase C subunit so as to promote cell prolification, while antagonists may be used to prevent or treat disorders related to excessive cell prolification, such as cancers. For example, mammalian cells or micelles expressing V-ATPase C subunit may be cultured together with labeled V-ATPase C subunit in the presence of a candidate compound and the ability of the compound to enhance or inhibit the interaction are tested.
Antagonists of V-ATPase C subunit include antibodies, other compounds, receptor deletant and analogs etc. These antagonists are capable of combining with human V-ATPase C subunit protein and eliminating its functions, or inhibiting expression of human V-ATPase C subunit, or binding with its active site so as to cause a loss of its biological functions. These antagonists may be used for the treatment of diseases resulted from disorders of cell proliferation, such as cancers.